Molecular identification of an enzyme reported over 60 years ago

From the 1950s to 1970s, discovery of enzymes began by identifying new chemical reactions within cell-free extracts, but their molecular identification among (function unknown) hypothetical genes (proteins) is difficult. Sugar acids are compounds formed by the oxidation of aldose monosaccharides. Metabolic genes for C4 and C5/C6 sugar acids are separately located on bacterial genomes. However, researchers discovered that in several bacteria, including the marine bacterium Paracoccus litorisediminis, these genes form a single cluster, in which a homologous gene to GL300_RS07945 was usually contained. GL300_RS07945, belonging to SDR protein superfamily, was a typical "function unknown gene" with less than 30% amino acid sequence similarity to any known functional protein.